Method of plating polonium



rays, and, during the course of its relatively short commercially, as a convenient and efllcient agent die-lead, consists mainly of lead, but contains smallamounts of..radium D and polonium. The usual commercial process of isolating polonium comprises forming a solution of a soluble salt,

' I plating the polonium from this solution onto anothermetal. Electroplating with applied voltage Patented Jan. is, 1944 UNITED STATES PATENT OFFICE Msrnon or 1:21:; roLonmM John H. Dillon, Akron,v Ohio, assignor to The Firestone Tire a Rubber Company,

Akron,

Ohio, a corporation of Ohio No Drawing. Application October 21, 1940,

Serial No. 362,061

scams- (Chin- 62) the uranium-radium family of radioactive el-' ments. It has a half-life period of about 138 days and is a powerful emitter ofstrong alpha rays. It emits practically no beta rays or gamma life it gradually changes directly into an inactive isotope of lead. By virtue of its unique properties polonium is utilized, both scientifically and for ionizing gases. An example of an important commercial use of polonium is the incorporation of an extremely small amount of the metal in an Po'lonium occurs in commercially significant K quantities in radio-lead compounds which are a by-product of the radium refining industry. Ra-

preferably the chloride, of radio-lead and then is not necessary, as thepolonium will plate onto most other metals by adsorption or chemical dis- 7 placement. 'According to a preferred procedure polonium is plated by chemical displacement from a hot;solution .01. radio-lead chloride onto nickel foils. The plated nickel foils may be used' directly, melted with or without the addition of other metal to form a polonium alloy,'or treated to drive off the free polonium (e, g., by vaporization) so that it may thereafter be isolated in a more concentrated form.

, of talging up a further quantity of polonium in a ties thereof, it is desirable to remove this lead oxide from the plated metal without appreciable I loss of polonium therefrom, if the metal is to be thereafter incorporated in an alloy. 7 It is, therefore, a primary object of the invention to provides practical method of removing surface impurities from a polonium plated metal without substantial loss of polonium therefrom.

Another object is to provide a method of treating a polonium-plated metal to renderit capable subsequent plating operation.

The above and further objects The invention comprises treating poloniumplated metal with nitric acid of a certain strength in order to remove therefrom undesired surface impurities, such as lead'oxide, without substantial loss of polonium from the metal. It has been discovered that a treatment of polonium-plated metal containing lead oxide with ordinary concentrated nitric acid containing about '70 per cent of HNOa removes all of the lead oxide together is no loss of polonium. Treatment of the metal Theradio-lead chloridefor the plating solution I is generally prepared by treating radio-lead ox-' ide with hydrochloric acid.- Freshlyprepared radie-lead chloride usuallycontains a slight amount of the unconverted lead oxide in a very finely d'ivlded form. yvhen such fresh preparation is used in a polonium platingbath, the finely dividride, freshly prepared from radio-lead oxide.

ed oxide deposits mechanically on the metal be- 59 ing plated. jThe polonium is distributed throughout the lead-oxide scale on the surfaces; oftlie metal; Since lead. is considered --very objection- I ablein nickel andotheralloy's, from the stand pointptthe p and the-physicalpropermadeup y adding partsblw m 010011- with acid containing about to per cent of- I-INO; completely removes the lead oxide from the plated metal without occasioning the loss of a substantial quantity of the polonium therefrom. Y

. The following examples arepresented for the purpose of illustrating specific applications of the invention and are not meant to be construed as limiting theinvention thereto. f

Nickel mus were plated withpolonium by-immersion in a boiling solution of radio-lead chloplated'foils were uniformly pink, because of the lead oxide precipitated thereon from theplating solution. The polonium contents of the foils were determined by a known method of measuring the alpha-ray of foils, andthen several foils were separately immersed in nitric acid of a definite strength for a short time. Thereafter the foils were rinsed with water, dried,

andexamined for freedom from leadoxide (free.-.

. dom from any pink appearance) and for any loss in content. Table I shows the results obtained with various concentrations of ENOa,

\ tent of the foils after treatment.

Table I Volume con- Per Per cent Removal centrated cent Immersion time less oi 01 lead acid to water HNQ: polonium oxide 100/0 70 Instantaneous.-- 87 Complete. 100/100 41 do .20 Do.. 100/125 37 30 seconds 3. 6 to d 7 Do. 100/150 34 6 to 60 seconds Not quite complete.

It is apparent from Table I that 34 per cent HNOa is-unsatisfactory, since it does not completely remove the lead oxide. The 70 per cent HNOa (ordinary concentrated nitric acid) is manifestly too concentrated; since it removes most of the polonium from the foils The 37 per cent acid is a. practical compromise, since it removes all of the,lead'oxide without removing much polonium. The 41 per cent acid is near the upper practical limit, in that it occasions the loss of about 20 per cent of the polonium. Therefore, a range of about 35, to about 40 per cent HNOzis preferred for treating the foils.

. Exmm 2' golonium-plated foils with surfaces contaminated with; lead oxide were cleaned by immersion in-appro'xim'ately 37 per cent nitric acid, in the manner set out in Example .1. TableII shows the change in the apparent polonium con- Table II Chaugein apparen polonium content Immersion time sen /7,108;- 7.9 gain. 8.1 gain.

30 seconds 30 seconds 180 seconds Theapparent again in polonium content of certain foils cleaned by immersion in the nitric acid bath can be readily explained on the as-- sumpti'on'that both the lead oxide and the sur-- face polonium initially dissolve in the nitric acid,

and then most of thedissolved polonium re-' plates onto the cleaned foil surface. Since there I is no longer any lead xide" present as a scale on EXAMPLE 3 Nickel foils were polonium-plated in the man.-

ner described in Example I and then cleaned of lead oxide by immersion in approximately 37 per cent nitric acid for 30 seconds. The foils.

were rinsed thoroughly with water and then placed in a fresh radio-lead chloride plating bath for a second plating. After the usual plating 10 period .the foils were examined and found to in the acid. Usually the oxide scale is pink, but occasionally it has-a black or'bluish cast.- Ordinary plated foils, having a light pink cast, are

. completely cleaned' by immersion for about 5' to 30 seconds in the nitric acid, whereas foils havinga. heavy deposit of oxide may. require immersion for as long as about three minutes.

Modification may be resorted to without ,departing from the scope and spirit of the invention as set forth in the appended claims.

What is claimed is;

1; The method of removing surface lead oxide from polonium-plated metal which comprises treating the plated metal with approximately 3'? per cent aqueous nitric acid.

. 2. The method of removing surface lead com- 7 pounds from'polonium-plated metal which. com-' prises treating the plated metal with 85 to 40 per cent aqueous HNO's.

3. Themethod of producing polonium-plated L metal havingan exceptionally high surface concentration of polonium which comprises the steps of plating polonium from a solution containing the same onto a metal, then treating the plated metal with 35 to 40 per' centaqueous HNOJ, and

thereafter plating a further quantity of polonium onto the .plated metal. JOHNH.DllhliClliL have approximately double the polonium content of foils plated only once. Plated foils con- The cleaning period is judged by the appearance'of the foils before and after immersion i 

